Current Therapy for Vascular Occlusive Diseases: Thrombosis and many related peripheral obstructive diseases are the result of abnormal activation of normal clotting mechanisms. Normal blood clotting is the result of a highly amplified chain reaction triggered by exposure of soluble factors and platelets to tissue factors, collagen and certain metabolites or hormones such as adenosine diphosphate (ADP), adrenaline and thromboxane. The clotting mechanism makes use of two systems: (a) soluble factors in the blood which activate each other in a serial manner causing hydrolysis of fibrinogen to fibrin which forms an insoluble crosslinked network, and (b) the circulating thrombocytes (platelets) which respond to the activating stimuli by releasing their own activators and by aggregating with each other. In normal clotting the soluble and platelet systems interact, with activation of one reinforcing the activation of the other. Abnormal activation of these systems can give rise to peripheral obstructive diseases. . While the pathogenesis is very complex, current models involve a lesion of the vein or artery wall, local activation of the clotting system, recruitment of activated soluble factors and platelets into the region, homeostasis, local ischemia, and reinforced activation recruitment.
The platelet plays a central role in the formation and extension of clot in both venous and arterial thrombosis. In venous thrombosis, the activation of platelet initiates shape changes and release reactions of platelet contents such ADP, arachidonic acid derivatives, clotting factors which promote platelet recruitment and aggregation and activate coagulation cascade leading to fibrin formation. The activated platelet also provides an activated surface (platelet factor III) which serves as a binding site for soluble clotting factors thereby increasing their interaction and further accelerating the rate of fibrin formation.
Current therapy for venous thrombosis relies mainly on the inhibition of fibrin formation; little attention was given to inhibition of the platelet which plays central role in activation. Conventional therapy for venous thrombosis makes use of heparin which actively neutralizes several of the activated soluble clotting factors. Conventional therapy also makes use of the so-called "oral anticoagulants" (dicumarol and related compounds) which inhibit the synthesis of these factors. Direct platelet activation is not affected by these drugs. In arterial thrombosis, platelets adhere to injured or diseased vessel wall and transform their shapes, release ADP and other platelet granule content, convert arachidonic acid to thromboxane A.sub.2, which promotes more platelet aggregation and vasconstriction and consolidation of platelet plugs. The use of antiplatelet drugs is, therefore, the mainstay of treatment and prevention of arterial thrombosis. Two classes of drug target the platelet and are used to treat arterial thrombosis: aspirin and dipyridamole. Aspirin inhibits the activation of arachidonic acid, which is one of the pathways for platelet activation. This offers some protection against activation. Dipyridamole is a phosphodiesterase inhibitor which increases the platelets' cyclic AMP level. This offers further protection against activation.
Extensive clinical trials on the use of these agents in arterial thombosis showed minimal therapeutic effects.
Ca.sup.2+ Entry Blockers Are Effective Anticoagulants: The above information suggests that it would be useful to be able to further inhibit the platelet contribution to the aggregation process. The present invention shows that increases in cytoplasmic Ca.sup.2+ concentration are central to the activation process. For instance, it has been demonstrated that platelets from patients with peripheral obstructive diseases have defects in their Ca.sup.2+ handling which gives rise to higher cytoplasmic and sequestered Ca.sup.2+ levels. This results in increased probability of recruitment of the platelet into the growing thrombus or diseased area. This Ca.sup.2+ handling defect can be corrected according to the present invention by medication with Ca.sup.2+ entry blockers; clinical improvement in the patient results. Currently-available methods are not capable of assessing these abnormalities because such testing methods are too insensitive to the Ca.sup.2+ handling defect. As disclosed herein, the action of the Ca.sup.2+ channel blockers is readily demonstrated using a fluorescent probe technique for the measurement of platelet-sequestered Ca.sup.2+.
Discovery of Ca.sup.2+ Entry Blockers; Cardiac and Smooth Muscle Effects: A large number of compounds, termed generically "Ca.sup.2+ -channel blockers" has seen widespread use in the control of angina and treatment of myocardial infarction. These are presently divided into three groups: (1) nifedipine and related 1,4-dihydropyridines, (2) verapamil and methoxyverapamil (D600), and (3) diltiazem and cinnarizine and related diphenylmethyl alkylamines. A cardiac-inhibitory function of verapamil was discovered by Fleckenstein (Fleckenstein, A., Tritthart, H., Fleckenstein, B., Herbst, A. and Grun, G., A new group of competitive Ca antagonists (Iproveratril, D600, Prenylamine) with high potent inhibitory effects on excitation-contraction coupling in mammalian myocardium (1969), Pfluegers Arch. 306:R25) who showed that this compound had inhibitory actions similar to the removal of extracellular Ca.sup.2+. Subsequently, he demonstrated that this action was shared with methoxyverapamil and nifedipine. He suggested that the compounds be termed "Ca.sup.2+ antagonists" and showed that the effects of these agents were to block the slow inward Ca.sup.2+ current during systole. Subsequently, the compounds were shown to inhibit Ca.sup.2+ influx into smooth muscle. These properties make the compounds very suitable for control of angina and treatment of myocardial infarction. The Ca.sup.2+ -channel blockers apparently exert their actions primarily at membrane potential-dependent Ca.sup.2+ channels. In smooth muscle, which can be stimulated both by membrane depolarization and noradrenaline or acetylcholine, the Ca.sup.2+ channel blockers are generally less effective against receptor-activated channels, sometimes requiring four orders of magnitude higher doses for 50% effectiveness. The literature shows that a given Ca.sup.2+ channel blocker will show different ED.sub.50 s for different tissues and that a given tissue will have different ED.sub.50 s for different channel blockers.
The present invention deals with the use of calcium channel blockers in diseases arising from platelet hyperactivation. Contemporary knowledge in the art has failed to establish a definite effect of the calcium channel blockers on the platelet and has a number of explanations each attributable to the conditions of the study and intricacies of the tested system. The test of Ca.sup.2+ -handling abnormalities used in the present application is more specific to the diseased state and to the mechanism of progression of peripheral obstructive disease.
We have discovered and hereby disclose method of treating peripheral obstructive diseases in patients requiring such treatment in which a Ca.sup.2+ channel blocker is administered to the patient for a period of time and in therapeutic quantities effective to relieve the disease symptoms and mitigate or remove the obstruction.
Also disclosed is a sensitive diagnostic procedure for assessing defection, abnormal Ca.sup.2+ handling of platelets which is indicative of certain peripheral obstructive diseases and, in turn, a means to assess a patient's response to Ca.sup.2+ channel blockers in the therapy of such diseases. Method for correcting the Ca.sup.2+ handling characteristics of blood platelets are also described.